VERITAS Volume Manager 3.5 Troubleshooting Guide (September 2004)

Recovery from Hardware Failure
Recovery from DCO Volume Failure
Chapter 1
26
Recovery from DCO Volume Failure
Persistent FastResync uses a data change object (DCO) log volume to perform tracking of
changed regions in a volume. If an error occurs while reading or writing a DCO volume,
it is detached and the badlog flag is set on the DCO. (You can use one of the options -a,
-F or -m to vxprint to check if the badlog flag is set on a DCO.) All further writes to the
volume are not tracked by the DCO.
To recover the DCO volume, perform the following steps:
Step 1. Correct the problem that caused the I/O failure.
Step 2. Use the following command to remove the badlog flag from the DCO:
# vxdco -g diskgroup -o force enable dco
Step 3. Restart the DCO volume using the following command:
# vxvol -g diskgroup start dco_log_vol
Step 4. Use the vxassist snapclear command to clear the FastResync maps for the original
volume and for all its snapshots. This ensures that potentially stale FastResync maps
are not used when the snapshots are snapped back (a full resynchronization is
performed). FastResync tracking is re-enabled for any subsequent snapshots of the
volume.
CAUTION You must use the vxassist snapclear command on all the snapshots of the volume
after removing the badlog flag from the DCO. Otherwise, data may be lost or corrupted
when the snapshots are snapped back.
If a volume and its snapshot volume are in the same disk group, the following command
clears the FastResync maps for both volumes:
# vxassist -g diskgroup snapclear volume snap_obj_to_snapshot
Here snap_obj_to_snapshot is the name of the snap object associated with volume that
points to the snapshot volume.
If a snapshot volume and the original volume are in different disk groups, you must
perform a separate snapclear operation on each volume:
# vxassist -g diskgroup1 snapclear volume snap_obj_to_snapshot
# vxassist -g diskgroup2 snapclear snapvol snap_obj_to_volume
Here snap_obj_to_volume is the name of the snap object associated with the snapshot
volume, snapvol , that points to the original volume.
Step 5. To snap back the snapshot volume on which you performed a snapclear in the previous
step, use the following command (after using the vxdg move command to move the
snapshot volume back to the original disk group, if necessary):
# vxplex -f -g diskgroup snapback volume snapvol_plex